The objective of this research project is to compare the chemical structures of alpha1-protease inhibitor among human genetic variants, and to determine the chemical basis for the microheterogeneity of the protein. The structure-function relationship of alpha1-protease inhibitor will be investigated by chemical modifications of the protein and by comparing the chemical structures of the protein isolated from a variety of organisms. Finally, the mechanism of interaction between alpha1-protease inhibitor and the proteases will be investigated. These studies are made possible by first establishing the complete covalent structure of the protein.